welcome to the best reefing site in the world.unlimited info on any question you may have.if not for reef2 reef I would probably have a gold fish tank and a betta on the counter.
that's not an easy question to figure out.i use a 40gal top off tank with 2 tsp per gallon of kalk.per gallon.it's a well established system with a large need for cal and alk.i mainly use the kalk for alk sense it does not provide enough cal.for the system.for cal I use aquaforest to maintain a level around 420 or so.
for you I would recommend starting out with a tsp or less per gallon to start and test test test till you get your levels to your liken.every system is different.the more corals the more they will use.once your evaporation rate can not keep up with your consumption of cal.and alk it's time to use some kind af additional dosing.you will only find that out by testing the levels on a weekly or bi weekly schedule.start slow and keep an eye on it.